A condenser microphone is configured so that an electrostatic acousto-electric converter in which a diaphragm and a backplate are arranged opposedly is included in a microphone unit, and an impedance converter such as a field effect transistor (FET) is incorporated because of its very high impedance. Usually, in the condenser microphone, a phantom power source is used, and microphone sound signals are delivered via a balanced shielded cable for the phantom power source.
To connect the balanced shielded cable, a 3-pin type output connector, for example, specified in EIAJ RC-5236 “Latch Lock Type Round Connector for Audio Equipment” is provided on the microphone casing side. By this output connector, the balanced shielded cable can be attached to and detached from the condenser microphone.
If strong electromagnetic waves radiated from a cellular phone or the like are applied to a microphone casing or a microphone cable in the state in which the balanced shielded cable is connected to the output connector, a which the balanced shielded cable is connected to the output connector, a high-frequency current inherent in the electromagnetic waves intrudes into the microphone casing through the output connector, and sometimes is detected by the impedance converter or the like and is delivered from the microphone as audible frequency noise.
As one method for preventing the generation of this kind of noise, the present applicant has proposed an output connector of microphone having a shielding function in Japanese Patent Application Publication No. 2005-311752. The configuration of this output connector is explained with reference to FIGS. 5 and 6. FIG. 5A is a front view of the output connector, in which only a shield cover is shown as a cross section, FIG. 5B is a sectional view taken along the line B-B of FIG. 5A, FIG. 6A is a lower plan view of a printed wiring board disposed on the output connector, and FIG. 6B is an upper plan view of the printed wiring board.
An output connector 10 includes a disc-shaped connector base 11 consisting of an electrical insulator such as PBT (polybutylene terephthalate) resin. In the connector base 11, three pins of a first pin E for earthing, a second pin SH on the hot side of signal, and a third pin SC on the cold side of signal are provided, for example, by press fit.
In this specification, the first pin E for earthing is sometimes referred simply to as the “earthing pin E”, and the second pin SH on the hot side of signal and the third pin SC on the cold side of signal are sometimes referred simply to as the “signal pin SH” and “signal pin SC”, respectively.
As shown in FIG. 5B, the output connector 10 is mounted in an end portion of a microphone casing (microphone grip for the handheld microphone), not shown, via a connector housing 20. The connector housing 20 consists of a cylindrical body made of a metal such as a brass alloy, and also functions as the shield casing of the output connector.
In the connector base 11, an internally threaded hole 13 is formed toward the inside in the radial direction from the outer peripheral surface thereof. In the internally threaded hole 13, a male screw 12 for fixing the output connector 10 to the connector housing 20 is threadedly mounted.
According this configuration, as shown in FIG. 5B, by using a screwdriver or the like, not shown, through a round hole 21 formed in the connector housing 20, the male screw 12 is turned, pulled out to the outside in the radial direction, and caused to butt against the peripheral edge of the round hole 21. Thereby, the output connector 10 can be fixed firmly to the connector housing 20.
In fixing the output connector 10 in the connector housing 20, the earthing pin E is electrically connected to the connector housing 20 serving as the earth via a conductive member such as a plate spring, not shown.
According to Japanese Patent Application Publication No. 2005-311752, to prevent electromagnetic waves radiated from a cellular phone or the like from intruding into the microphone casing, a printed wiring board 14 and a shield cover 15 are provided on the base inner surface (the surface arranged on the inside of microphone, the upper surface in FIGS. 5A and 5B) side of the connector base 11.
The printed wiring board 14 is a double-sided printed board having three insertion holes 141, 142 and 143 through which the earthing pin E and the signal pins SH and SC penetrate. As shown in FIG. 6A, on a lower surface (a surface facing the connector base) 14B of the printed wiring board 14, a shield layer 144 consisting of a copper foil solid pattern is formed. The shield layer 144 is formed so as to exclude portions around the insertion holes 142 and 143 through which the signal pins SH and SC are inserted.
As shown in FIG. 6B, on an upper surface 14A of the printed wiring board 14, a shield electrode 145 is formed throughout the entire periphery thereof. The shield electrode 145 and the shield layer 144 on the lower surface side are connected electrically to each other via plating in a plurality of through holes 146.
The through hole plating is also applied in the insertion hole 141. The earthing pin E is electrically connected to the shield layer 144 via the through hole plating in the insertion hole 141. In the insertion holes 142 and 143 as well, the through hole plating is applied to ensure the electrical connection with the signal pines SH and SC.
In this example, the pin insertion hole 141 for the earthing pin E is connected to two locations of the shield electrode 145 by lead wires 147a and 147b extending from the edge of the pin insertion hole 141 to the directions opposite to each other.
Also, the pin insertion holes 142 and 143 for the signal pins SH and SC are connected to the shield electrode 145 by lead wires 147c and 147d, respectively. In an intermediate portion of each of the lead wires 147c and 147d, a capacitor element 148 and a Zener diode element 149 are mounted in parallel.
That is, to between the earthing pin E and the signal pin SH and to between the earthing pin E and the signal pin SC, the capacitor element 148 and the Zener diode element 149 are connected in parallel. The capacitor element 148 prevents intrusion of high-frequency waves. The Zener diode element 149 prevents circuit destruction due to static electricity.
The shield cover 15 includes a ceiling part 151 that covers the upper surface 14A of the printed wiring board 14 and a skirt part 152 that is fitted on the outer peripheral surface of the connector base 11. In the ceiling part 151, three through holes through which the earthing pin E and the signal pins SH and SC penetrate are formed.
Among these through holes, the through hole for the earthing pin E is formed as a hole having a diameter approximately equal to the diameter of the earthing pin E so as to be capable of being in contact with the earthing pin E to electrically connect the earthing pin E and the shield cover 15 to each other. The earthing pin E is soldered to the shield cover 15.
The through holes for the signal pins SH and SC are formed so as to have diameters larger than the diameters of the signal pins SH and SC so as to be in noncontact with the pins. These through holes are preferably formed so as to have diameters as small as possible to restrain the leak of a high-frequency magnetic field, which is generated from the wiring portion and the like, into the microphone casing to a minimum when the high-frequency current flows in the capacitor element 148.
According to the output connector 10 having the above-described configuration, double shield is formed by the shield layer 144, which consists of the copper foil solid pattern formed on printed wiring board 14, and the shield cover 15. Also, by the capacitor element 148 mounted on the printed wiring board 14, the intrusion of the high-frequency current caused by electromagnetic waves coming through the signal pins SH and SC can be inhibited.
Also, the capacitor element 148 and the Zener diode element 149 are mounted in parallel, and when a current flows from the signal pin SH, SC side toward the earthing pin E, the current flows in the Zener diode element 149, and then flows in the capacitor element 148. Therefore, the capacitor element 148 can be protected from electrostatic destruction.
Recently, concerning the prevention of the generation of noise caused by extraneous electromagnetic waves, it has been demanded that noise be not generated even in a situation where electromagnetic waves having a high field intensity of, for example, about 1 GHz is applied to the microphone. To meet this demand, the countermeasures using electrostatic shield in the conventional example are insufficient.
Accordingly, in the Japanese Patent Application Publication No. 2010-067711, the present applicant has proposed that a magnetic sheet is provided additionally on the shield cover 15. According to this configuration, due to the high-frequency magnetic field generated in the capacitor element 148, a high-frequency current is caused to flow by induction in the printed wiring board for sound signal output in the microphone casing and the circuit parts mounted on the printed board, so that the generation of noise can be prevented.
On the other hand, the printed wiring board 14 is provided with the Zener diode element 149 in parallel with the capacitor element 148. Especially in a situation where the printed wiring board 14 is exposed to higher-frequency and strong field intensity, the Zener diode element also poses a problem.
That is, since the Zener diode element is also a semiconductor non-linear element, when strong electromagnetic waves are applied to a microphone cable, the high-frequency current caused by the electromagnetic waves is detected, and audible frequency noise is sometimes generated.
Accordingly, an object of the present invention is to provide an output connector for a condenser microphone, which has a printed wiring board mounted with a capacitor element for preventing intrusion of high-frequency waves and a Zener diode element for preventing circuit destruction due to static electricity and is configured so that the generation of noise caused by the Zener diode element is reduced.